Please help need advice!!!

[Andres]

So I am very concerned about port matching the GT80 cylinder with my stock crank transfer ports.My concern is I am running stock cdi and a 6cc high compression head.Do you think it will start if it does will it run without a problem.Do you recomend I upgrade to this cdi below???

 

[crassius]

it is stroke and rod length that will need to be matched - ignition timing won't change

 

[Deleted member 12676]

any good engine builder will tell you that when you increase the compression you need to retard the ignition.
The Lightning is more retarded than standard but not as much as the Jaguar CDI.
These engines need a 7.5cc head. Anything less gives too much compression which will cause the cylinder plating to flake off and the bearings to have a short life.

 

[Andres]

any good engine builder will tell you that when you increase the compression you need to retard the ignition.
The Lightning is more retarded than standard but not as much as the Jaguar CDI.
These engines need a 7.5cc head. Anything less gives too much compression which will cause the cylinder plating to flake off and the bearings to have a short life.

W
Were can I by a jaguar cdi and a 7.5cc head

 

[Deleted member 12676]

Click on my signature link to go to my site and go to the CDI page.
I don't think anyone makes a 7.5cc head which is one reason I stay mad at all of the parts suppliers.
If anyone knows of one then please inform us.
If there is none then you can sandpaper down the stock head about .8mm or buy a 7cc head and dremel out more space in the combustion bowl. Either way you'll need a pressure gauge to make sure you don't exceed 130psi.

 

[Andres]

Click on my signature link to go to my site and go to the CDI page.
I don't think anyone makes a 7.5cc head which is one reason I stay mad at all of the parts suppliers.
If anyone knows of one then please inform us.
If there is none then you can sandpaper down the stock head about .8mm or buy a 7cc head and dremel out more space in the combustion bowl. Either way you'll need a pressure gauge to make sure you don't exceed 130psi.

Thanks

 

[gary55]

These heads do not increase compression unless replacing a stock straight plug head. Left to right stock straight plug head = 10.1cc, stock slant plug head = 6cc, pancake performance head = 7.9cc, rounded fin performance head = 8cc, flat fin performance head = 8cc. The head on the far right is the head sent with the GT 80 engines. I am not real smart on the various performance gains achieved through the differing chamber designs. I can tell you that the gains are not due to increased compression. The slant plug head has the highest compression of all the heads below.

 

[sp1ke]

nothing to bad in port matching apart from changing the volume of the crank case

removing material weakens your compression in your crank and thusly at your head so reducing the force thrusting up the transfers

so you may get away with that head making up the loss in theory wouldnt run just that head on standard bike jag is right could put compression to high he knows his stuff dont exceed 130 psi

but with a weakened initial compression its possible id definatly do some compression tests

 

[gary55]

Surely by now you have completed this build. I would love to hear what your compression was. If you didn't remove any material from the head or cylinder it should be around 90 lbs.. I have built 5 of these engines so far. They need around .030 decked from the jug to get to 125lbs. comp.. This is all assuming that the bottom end you are putting it on is type B with 40mm stroke. If you are putting it on a type A bottom end you will have problems. So how did the build go?

 

[Andres]

Surely by now you have completed this build. I would love to hear what your compression was. If you didn't remove any material from the head or cylinder it should be around 90 lbs.. I have built 5 of these engines so far. They need around .030 decked from the jug to get to 125lbs. comp.. This is all assuming that the bottom end you are putting it on is type B with 40mm stroke. If you are putting it on a type A bottom end you will have problems. So how did the build go?

It went really good but i cant get the engine to pass 45mph